The long-term goal of this project is to better understand the assembly and regulation of the urothelial plaques that cover almost the entire apical surface of mammalian urothelium. These plaques represent two dimensional crystals of hexagonally arranged 16-nm particles, that are composed of four major integral membrane proteins called uroplakins. It has been assumed that urothelial plaques are rigid structures that are overlaid by a glyco-calyx or mucin layer which plays a role in forming the permeability barrier and/or in inhibiting the attachment of uropathogenic E. coli. Recent negative staining and quick-freeze deep-etch (QFDE) data suggest that each 16-nm particle is a mushroom-like structure consisting of a 16-nm propeller-like head anchored into the lipid bilayer of the plaque via a narrower 9-nm tail; that the plaque structure is in dynamic flux undergoing breakage and reformation; and that the apical surface of the mouse urothelial plaques are not covered by an extensive glycocalyx. This project will perform four series of experiments to determine (i) whether the apical urothelial surface of mammalian bladder exhibits species-dependent variations; (ii) how the uroplakin particles are delivered to the apical surface during wound healing; (iii) whether the size of the urothelial plaques are adjusted reversibly during different phases of the micturition cycle; and (iv) whether urothelial plaques are heterogeneous in their uroplakin composition. These studies will shed light on the heterogeneity of urothelia, the appropriateness of some of the animal models for studying urinary tract infections, the mechanism of permeability barrier and self-defense against infections, the mode by which the cytoplasmic AUM vesicles are assembled and regulated during normal and hyperplastic urothelial differentiation, the dynamic nature of urothelial plaques, and the uroplakin composition of individual urothelial plaques. The data may also have implications on the pathophysiological bases of important bladder diseases including interstitial cystitis and urinary tract infections.